Shunt regulators

[edy252]

hi all...

i was wondering what type of shunt regulators to use....i expect a MAXIMUM of 55 amps (which i probably would never see!!! )

thx in advance

[kirk]

you need to know power, not just current.

[edy252]

55 amps at 12 volts (660 watts)

[kirk]

55 x 12 = 660 watts or 2253 BTU per hour.

You will need a large heatsink to keep temperature riser reasonable if you use a solid state load.

It may make sense to use resistors and switches in the interest of reliability.

Resistors are not as sensitive to heat as semiconductors are. If I was going to use a solid state dynamic load I would use FETs as they are free of secondary breakdown and also share loads easier.

As for a stepped load 7 resistors and 7 switches gives you 128 binary loads, less than 1% steps.

[Ungrounded Lightning Rod]

It may make sense to use resistors and switches in the interest of reliability.  Resistors are not as sensitive to heat as semiconductors are.

You can also increase their power handling ability by a large factor by immersing them in a large can of transformer oil.  Hams have used this hack to make dummy loads for high-powered transmitters for years.

Or use old auto headlights.

Regardless, you have to GET RID of that heat somewhere eventually, and 660 watts is a third of a big space heater.  If you don't want your garage/battery shack/whatever to get way hot or catch fire in the summer, be sure to dump the heat outside.

Try fan-cooling the load.  Dump the heat out a dryer vent in the summer, add it to your room heating in the winter.  (You've got power to waset on a fan any time your load is being used.)  Or put a suitable electric element into your hot water heater and dump it there.  (If it gets TOO hot the relief valve will go.)

Heck:  Use a big fan to blow some air around.  THAT will dump the excess power - right back where it came from.  B-)

Or use it to pump some water out of your well into a ground-level or elevated storage tank.

There's lots of stuff to do with excess power.

[windrules]

Hi guys I think getting rid of the power is easy but to do it automaticly is a bit different.What simple cicuit can you use to do the switching(I'm no electician but can follow instrucions OK)

regards,

Mos

[hvirtane]

I think that the easiest method is to use a simple

relay. You can measure how high up your generator

is able to push the voltage, when the battery

is already full and the generator is pushing

in more.

The relay will be adjusted such a way

that it will connect a dump load at the time,

when the voltage across the battery is

higher than the voltage of the full battery.

When the generator

is pushing the voltage across the battery

higher than the desired voltage

the relay will connect the dump load

and when the generator stops,

it will disconnect the dump load.

- Hannu

[Ungrounded Lightning Rod]

I think that the easiest method is to use a simple relay. You can measure how high up your generator is able to push the voltage, when the battery is already full and the generator is pushing in more.

You have to have "hysteresis":  The relay has to pull in at one voltage and drop out at another, lower voltage.  Otherwise the voltage drop from turning on the dump load will cause the relay to chatter.

An easy way is to sense, not the charging voltage, but the voltage at the tap between two resistors, one connected to the battery, one to the dump load.  Adjust the ratio of the resistors to give you the desired hysteresis.

Two or three resistors, a zener, a transistor, and a relay will do the job, and have a rather small leakage when the relay is off.

[windrules]

thanks Ungrounded but do you or someone else have a simple diagram on how to put this relay together, also i guess if the load is high you could just ad relays in parrallel,

thanks,

Mos

[kurt]

do view image to see full size diagram